Bisphenol-A production is commonly done by reacting phenol and acetone using strong acid sulfonated styrene/divinylbenzene ion exchange resin catalysts, which are partially neutralized with mercaptoamine promoters. Methanol and other aliphatic alcohols are typically present in small amounts in the acetone raw material, and are believed to deactivate mercaptoamine-promoted bisphenol-A catalysts.
In a bisphenol-A production process, distillation is typically used to remove acetone and water from either the reactor effluent or the mother liquor from a phenol/bisphenol adduct crystallization step. This distillation step also removes methanol and other alcohols with the acetone and water, and some phenol and bisphenol may also be codistilled. This first distillation step is commonly referred to as the “drying column” or “lights removal column.” A second distillation step is also typically used to recover acetone from the aqueous acetone mixture from the first distillation step. This second distillation step is commonly referred to as the “acetone recovery column.” Typically, the methanol is also codistilled with the acetone, and the recovered methanol-containing acetone is recycled to the reactor for reuse. Since methanol does not readily react in a bisphenol-A process, this recycling can result in the accumulation of methanol in the process, which accelerates the deactivation of the catalyst. It would, therefore, be desirable to remove methanol from the bisphenol-A process to prevent deactivation of the catalyst.
EP 1 683 779 A1 discloses a process for producing bisphenol A wherein said process inhibits deterioration of the cation exchange resin catalyst used in the reaction step to prolong the catalyst life by reducing the lower alcohols such as methanol contained as impurities in acetone which is used as one of the raw materials. WO 2007/086239 A1 also discloses a bisphenol A production method which prevents a decline in bisphenol A production catalyst activity in the bisphenol A production method step in which the impurities present in a portion of the mother liquor obtained in a bisphenol A separation step are treated and the mother liquor is subsequently re-supplied to the reaction system. Neither of the above two references disclose a method of separating methanol from acetone recycle streams during production of bisphenol-A in a single acetone recovery distillation column, wherein a substantial amount of methanol leaves with the bottoms product form the bottom section of the distillation column.
Distillative separation of methanol from acetone is known to be difficult, due to the formation of azeotropes. Several alternatives for separating methanol from acetone have been proposed, including adsorption, reaction of methanol with another chemical followed by distillation, and extractive distillation using another extractive agent. However, each of these potential solutions would likely require additional equipment and/or the introduction of additional chemicals to the process. Further, these solutions would be expensive to implement. Thus, there is a continuing need for a low-cost and easy-to-implement solution for removing methanol from a bisphenol-A production process.